Telomerase reverse transcriptase induces targetable alterations in glutathione and nucleotide biosynthesis in glioblastomas.

Unlabelled: Telomerase reverse transcriptase (TERT) is essential for glioblastoma (GBM) proliferation. Delineating metabolic vulnerabilities induced by TERT can lead to novel GBM therapies. We previously showed that TERT upregulates glutathione (GSH) pool size in GBMs.

Imaging telomerase reverse transcriptase expression in oligodendrogliomas using hyperpolarized δ-[1-C]-gluconolactone.

Background: Telomere maintenance by telomerase reverse transcriptase (TERT) is essential for immortality in most cancers, including oligodendrogliomas. Agents that disrupt telomere maintenance such as the telomere uncapping agent 6-thio-2'-deoxyguanosine (6-thio-dG) are in clinical trials. We previously showed that TERT expression in oligodendrogliomas is associated with upregulation of glucose-6-phosphate dehydrogenase (G6PD), the rate-limiting enzyme of the pentose phosphate pathway (PPP).

Hyperpolarized δ-[1- C]gluconolactone imaging visualizes response to TERT or GABPB1 targeting therapy for glioblastoma.

TERT promoter mutations are a hallmark of glioblastoma (GBM). Accordingly, TERT and GABPB1, a subunit of the upstream mutant TERT promoter transcription factor GABP, are being considered as promising therapeutic targets in GBM. We recently reported that the expression of TERT or GABP1 modulates flux via the pentose phosphate pathway (PPP).

A C/P surface coil to visualize metabolism and energetics in the rodent brain at 3 Tesla.

Purpose: We constructed a C/P surface coil at 3 T for studying cancer metabolism and bioenergetics. In a single scan session, hyperpolarized C-pyruvate MRS and P MRS was carried out for a healthy rat brain.

Methods: All experiments were carried out at 3 Tesla.

Deuterium Metabolic Imaging Reports on TERT Expression and Early Response to Therapy in Cancer.

Purpose: Telomere maintenance is a hallmark of cancer. Most tumors maintain telomere length via reactivation of telomerase reverse transcriptase (TERT) expression. Identifying clinically translatable imaging biomarkers of TERT can enable noninvasive assessment of tumor proliferation and response to therapy.

Imaging biomarkers of TERT or GABPB1 silencing in TERT-positive glioblastoma.

Background: TERT promoter mutations are observed in 80% of wild-type IDH glioblastoma (GBM). Moreover, the upstream TERT transcription factor GABPB1 was recently identified as a cancer-specific therapeutic target for tumors harboring a TERT promoter mutation. In that context, noninvasive imaging biomarkers are needed for the detection of TERT modulation.

Deuterium magnetic resonance spectroscopy enables noninvasive metabolic imaging of tumor burden and response to therapy in low-grade gliomas.

Background: The alternative lengthening of telomeres (ALT) pathway is essential for tumor proliferation in astrocytomas. The goal of this study was to identify metabolic alterations linked to the ALT pathway that can be exploited for noninvasive magnetic resonance spectroscopy (MRS)-based imaging of astrocytomas in vivo.

Methods: Genetic and pharmacological methods were used to dissect the association between the ALT pathway and glucose metabolism in genetically engineered and patient-derived astrocytoma models.

Acquisition and quantification pipeline for in vivo hyperpolarized C MR spectroscopy.

Purpose: The goal of this study was to combine a specialized acquisition method with a new quantification pipeline to accurately and efficiently probe the metabolism of hyperpolarized C-labeled compounds in vivo. In this study, we tested our approach on [2- C]pyruvate and [1- C]α-ketoglutarate data in rat orthotopic brain tumor models at 3T.

Methods: We used a multiband metabolite-specific radiofrequency (RF) excitation in combination with a variable flip angle scheme to minimize substrate polarization loss and measure fast metabolic processes.

Deuterium Metabolic Imaging-Rediscovery of a Spectroscopic Tool.

The growing demand for metabolism-specific imaging techniques has rekindled interest in Deuterium (H) Metabolic Imaging (DMI), a robust method based on administration of a substrate (glucose, acetate, fumarate, etc.) labeled with the stable isotope of hydrogen and the observation of its metabolic fate in three-dimensions. This technique allows the investigation of multiple metabolic processes in both healthy and diseased states.

Imaging 6-Phosphogluconolactonase Activity in Brain Tumors Using Hyperpolarized δ-[1-C]gluconolactone.

Introduction: The pentose phosphate pathway (PPP) is essential for NADPH generation and redox homeostasis in cancer, including glioblastomas. However, the precise contribution to redox and tumor proliferation of the second PPP enzyme 6-phosphogluconolactonase (PGLS), which converts 6-phospho-δ-gluconolactone to 6-phosphogluconate (6PG), remains unclear. Furthermore, non-invasive methods of assessing PGLS activity are lacking.

Metabolic imaging detects elevated glucose flux through the pentose phosphate pathway associated with TERT expression in low-grade gliomas.

Background: Telomerase reverse transcriptase (TERT) is essential for tumor proliferation, including in low-grade oligodendrogliomas (LGOGs). Since TERT is silenced in normal cells, it is also a therapeutic target. Therefore, noninvasive methods of imaging TERT are needed.

Early Noninvasive Metabolic Biomarkers of Mutant IDH Inhibition in Glioma.

Approximately 80% of low-grade glioma (LGGs) harbor mutant isocitrate dehydrogenase 1/2 (IDH1/2) driver mutations leading to accumulation of the oncometabolite 2-hydroxyglutarate (2-HG). Thus, inhibition of mutant IDH is considered a potential therapeutic target. Several mutant IDH inhibitors are currently in clinical trials, including AG-881 and BAY-1436032.

Non-invasive assessment of telomere maintenance mechanisms in brain tumors.

Telomere maintenance is a universal hallmark of cancer. Most tumors including low-grade oligodendrogliomas use telomerase reverse transcriptase (TERT) expression for telomere maintenance while astrocytomas use the alternative lengthening of telomeres (ALT) pathway. Although TERT and ALT are hallmarks of tumor proliferation and attractive therapeutic targets, translational methods of imaging TERT and ALT are lacking.

Ferronostics: Measuring Tumoral Ferrous Iron with PET to Predict Sensitivity to Iron-Targeted Cancer Therapies.

Although cancer has been known for decades to harbor an insatiable appetite for iron, only recently has the chemistry emerged to exploit this altered state therapeutically, by targeting the expanded cytosolic labile iron pool (LIP) of the cancer cell. The state of the art includes therapies that react with the LIP to produce cytotoxic radical species (in some cases also releasing drug payloads) and molecules that exacerbate LIP-induced oxidative stress to trigger ferroptosis. Effectively implementing LIP-targeted therapies in patients will require biomarkers to identify those tumors with the most elevated LIP and thus most likely to succumb to LIP-targeted interventions.

Glutamate Is a Noninvasive Metabolic Biomarker of IDH1-Mutant Glioma Response to Temozolomide Treatment.

Although lower grade gliomas are driven by mutations in the isocitrate dehydrogenase 1 (IDH1) gene and are less aggressive than primary glioblastoma, they nonetheless generally recur. IDH1-mutant patients are increasingly being treated with temozolomide, but early detection of response remains a challenge and there is a need for complementary imaging methods to assess response to therapy prior to tumor shrinkage. The goal of this study was to determine the value of magnetic resonance spectroscopy (MRS)-based metabolic changes for detection of response to temozolomide in both genetically engineered and patient-derived mutant IDH1 models.

In vivo detection of γ-glutamyl-transferase up-regulation in glioma using hyperpolarized γ-glutamyl-[1-C]glycine.

Glutathione (GSH) is often upregulated in cancer, where it serves to mitigate oxidative stress. γ-glutamyl-transferase (GGT) is a key enzyme in GSH homeostasis, and compared to normal brain its expression is elevated in tumors, including in primary glioblastoma. GGT is therefore an attractive imaging target for detection of glioblastoma.

PI3K/mTOR inhibition of IDH1 mutant glioma leads to reduced 2HG production that is associated with increased survival.

70-90% of low-grade gliomas and secondary glioblastomas are characterized by mutations in isocitrate dehydrogenase 1 (IDHmut). IDHmut produces the oncometabolite 2-hydroxyglutarate (2HG), which drives tumorigenesis in these tumors. The phosphoinositide-3-kinase (PI3K)/mammalian target of rapamycin (mTOR) pathway represents an attractive therapeutic target for IDHmut gliomas, but noninvasive indicators of drug target modulation are lacking.

In vivo investigation of hyperpolarized [1,3-C]acetoacetate as a metabolic probe in normal brain and in glioma.

Dysregulation in NAD/NADH levels is associated with increased cell division and elevated levels of reactive oxygen species in rapidly proliferating cancer cells. Conversion of the ketone body acetoacetate (AcAc) to β-hydroxybutyrate (β-HB) by the mitochondrial enzyme β-hydroxybutyrate dehydrogenase (BDH) depends upon NADH availability. The β-HB-to-AcAc ratio is therefore expected to reflect mitochondrial redox.

HDAC inhibition in glioblastoma monitored by hyperpolarized C MRSI.

Vorinostat is a histone deacetylase (HDAC) inhibitor that inhibits cell proliferation and induces apoptosis in solid tumors, and is in clinical trials for the treatment of glioblastoma (GBM). The goal of this study was to assess whether hyperpolarized C MRS and magnetic resonance spectroscopic imaging (MRSI) can detect HDAC inhibition in GBM models. First, we confirmed HDAC inhibition in U87 GBM cells and evaluated real-time dynamic metabolic changes using a bioreactor system with live vorinostat-treated or control cells.

Mutant IDH1 gliomas downregulate phosphocholine and phosphoethanolamine synthesis in a 2-hydroxyglutarate-dependent manner.

Background: Magnetic resonance spectroscopy (MRS) studies have identified elevated levels of the phospholipid precursor phosphocholine (PC) and phosphoethanolamine (PE) as metabolic hallmarks of cancer. Unusually, however, PC and PE levels are reduced in mutant isocitrate dehydrogenase 1 (IDHmut) gliomas that produce the oncometabolite 2-hydroxyglutarate (2-HG) relative to wild-type IDH1 (IDHwt) gliomas. The goal of this study was to determine the molecular mechanism underlying this unusual metabolic reprogramming in IDHmut gliomas.

2-Hydroxyglutarate-Mediated Autophagy of the Endoplasmic Reticulum Leads to an Unusual Downregulation of Phospholipid Biosynthesis in Mutant IDH1 Gliomas.

Tumor metabolism is reprogrammed to meet the demands of proliferating cancer cells. In particular, cancer cells upregulate synthesis of the membrane phospholipids phosphatidylcholine (PtdCho) and phosphatidylethanolamine (PtdE) in order to allow for rapid membrane turnover. Nonetheless, we show here that, in mutant isocitrate dehydrogenase 1 (IDHmut) gliomas, which produce the oncometabolite 2-hydroxyglutarate (2-HG), PtdCho and PtdE biosynthesis is downregulated and results in lower levels of both phospholipids when compared with wild-type IDH1 cells.

Clonal expansion and epigenetic reprogramming following deletion or amplification of mutant .

mutation is the earliest genetic alteration in low-grade gliomas (LGGs), but its role in tumor recurrence is unclear. Mutant IDH1 drives overproduction of the oncometabolite d-2-hydroxyglutarate (2HG) and a CpG island (CGI) hypermethylation phenotype (G-CIMP). To investigate the role of mutant IDH1 at recurrence, we performed a longitudinal analysis of 50 mutant LGGs.

Mutant IDH1 Expression Drives TERT Promoter Reactivation as Part of the Cellular Transformation Process.

Mutations in the isocitrate dehydrogenase gene IDH1 are common in low-grade glioma, where they result in the production of 2-hydroxyglutarate (2HG), disrupted patterns of histone methylation, and gliomagenesis. IDH1 mutations also cosegregate with mutations in the ATRX gene and the TERT promoter, suggesting that IDH mutation may drive the creation or selection of telomere-stabilizing events as part of immortalization/transformation process. To determine whether and how this may occur, we investigated the phenotype of pRb-/p53-deficient human astrocytes engineered with IDH1 wild-type (WT) or R132H-mutant (IDH1) genes as they progressed through their lifespan.